Large housings for transmissions are cast and then machined to close tolerances required to mount transmission gears, clutches and other critical components. Conventional machining lines for transmission housings cool and lubricate the housing with a flood of a water/oil emulsion coolant in both the rough and finish machining steps. A considerable amount of heat is created during the rough boring and face milling operation that builds up in the housing and in the chips machined from the housing. The flood of the water/oil emulsion coolant was formerly thought to be essential to cool the housing and wash large volumes of the hot chips from the part and tool.
Large amounts of water/oil emulsion coolant necessitate large coolant circulation systems for removing chips and cooling the recirculated coolant. The coolant and chips add to the waste disposal load of a plant and increase processing costs. Water/oil emulsion coolants can be recycled. Metallic cutting chips reclaimed from the coolant can be salvaged but at a reduced value compared to chips produced in a dry metal cutting operation. Coolant circulation systems are costly and require valuable manufacturing floor space. Operation of the water/oil emulsion coolant systems uses substantial energy.
Minimum quantity lubrication (MQL) systems have been developed that provide mist lubrication in air for milling, drilling, and tapping relatively small features that are less than 200 mm in diameter of a transmission housing. The bottom area of the transmission housing that is enclosed by the transmission fluid pan is processed through milling, drilling, and tapping operations with the bottom area inverted to provide easier access. MQL systems were not developed for rough boring and finish boring machines because of the heat generated by the boring and face milling operations. The hot chips removed from the housing contribute to the heat load. Flood cooling was previously thought to be the only way to provide cooling to the housing and lubrication to the boring and face milling machines.
Dedicated boring machines having large boring bars equipped with multiple cutting tools are used to machine large housings having inner diameters to be bored and faces to be milled that are more than 200 mm in diameter, such as a rear wheel drive transmission cases, and the like. Dedicated boring bar machines are expensive to purchase and require long purchasing lead times. Dedicated boring machines require substantial time for changeover to a different part or style of part and tooling changes result in long periods of line downtime. Dedicated boring machines on a machining line are normally part of a single path line so that if the boring machine requires servicing, the entire line is shut down.
The above problems and other problems are addressed by this disclosure as summarized below.